Page 22 - MetalForming July 2014

How to Improve
Spot-Welding Per formance
Resistance spot welding is a popular value-added secondary operation for many metalformers, but the process often is ignored until quality problems arise. When a customer calls to report that all the parts you just produced have been rejected due to bad spot welds, suddenly the process takes on a whole new level of importance.
BY TOM SNOW
Since weak spot welds may look similar to strong ones, how do you stay out of trouble? Here are some suggestions for improving your resistance spot-welding (RSW) per- formance, based on more than 40 years of experience.
1) Get trained on the RSW process.
Spot welding appears deceptively simple, but numerous process vari- ables must be understood and con- trolled. With many different settings available on the typical spot-welding machine, it’s important to understand how to adjust each setting for opti- mum results. And, just like baking a cake, it’s critical to use the right spot- welding recipe.
Metalformers should refer to readily available recipe charts, which prescribe the recommended settings for sec- ondary amps (weld heat), weld dura- tion (current flow time) and forging pressure (forc e) for spot welding vari- ous sheetmetal types and thicknesses. Note: Use these settings only as a start- ing point. A rule of thumb: Assuming the proper welding force is used, the strongest and most attractive joints typically result from a high heat setting and a short weld time, referred to as a Class A welding schedule.
Tom Snow is CEO of T. J. Snow Compa- ny, Inc., Chattanooga, TN, a manufac- turer, remanufacturer and distributor of resistance-welding machinery, supplies and accessories: 423/894-6234; www.tj- snow.com. He also serves as first vice chairman of the Resistance Welding Manufacturing Alliance, and heads its Education Committee.
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MetalForming/July 2014
www.metalformingmagazine.com
Although rocker-arm RSW machines are the most common due to their relatively low purchase price, they apply weld force with a lever action—the tips often skid if the arms are not perfectly aligned. Therefore, a more-expensive vertical-action press-type machine (shown) often gets the call when the application requires an attractive, low-marking show surface.